Check here first

There are a ton of places online to look for good guides on champions, have a look-see through these sites to see if your questions can be taken care of there.

MobaFire - By now one of the more popular sites for builds, not necessarily the cream of the crop but a decent choice.
http://www.mobafire.com/

LoL Wiki - It's a wiki, best for story and whatnot.
http://leagueoflegends.wikia.com/wik...f_Legends_Wiki

Solomid - Lots of great guides, keep in mind that the High Elo guides assume you're an advanced player.
http://www.solomid.net/guides.php

Leaguecraft - Personal first choice. Tons of guides, but seems to be getting a little dated. Also great tools for theory crafting.
http://www.leaguecraft.com/